Tungstophosphoric Acid-catalyzed Oxidative Desulfurization of Naphtha with Hydrogen Peroxide in Naphtha/Acetic Acid Biphasic System

Abstract

The 12-tungstophosphoric acid (TPA)-catalyzed oxidative desulfurization of naphtha with H2O2 was investigated. All organosulfur compounds examined were efficiently oxidized with H2O2 and TPA catalyst in acetic acid (AcOH). The order of the oxidation reactivities was sulfides, disulfides benzothiophenes thiophenes. Methyl substituents on benzothiophenes and thiophenes increased the reactivity of the sulfur atom. The major oxidation products from the organosulfur compounds, except a few thiophenes, were the corresponding sulfones. The organosulfur compounds in octane were also oxidized with H2O2 and TPA catalyst in an octane/AcOH biphasic system. The oxidation proceeded in the AcOH phase and most oxidation products remained in this phase, resulting in the successive removal of the sulfur compounds from the octane phase. Using this oxidative treatment effectively reduced the sulfur content of naphtha, as the sulfur content was reduced to about 0.5 mass ppm after adsorption with silica gel. Hydrodesulfurization is an effective pretreatment for oxidative desulfurization of naphtha, by which the sulfur content can be reduced to below 0.1 mass ppm.

Oxidative Desulfurization of Naphtha with Hydrogen Peroxide in Presence of Acid Catalyst in Naphtha/Acetic Acid Biphasic System

“…The difference in oxidation reactivities of MBs probably resulted from the promoting effect of the methyl substituent. A similar reactivity trend was observed in the tungstophosphoric acidcatalyzed oxidation with H2O2 13) .…”

“…Straight-run naphtha (NAP; boiling range, 343-424 K; S, 257 mass ppm) and hydrodesulfurized naphtha (NAPH; S, 11.3 mass ppm) were the same products as used in previous work 13) . AcOH and octane were used as solvents.…”

“…The concentration of the organosulfur compound was measured by the same high performance liquid chromatography (HPLC) method as before 13) .…”

“…On the other hand, the oxidative treatments of NAP resulted in large reductions in the sulfur content of NAPO from 257 mass ppm to less than about 12 mass ppm, indicating that this oxidative treatment would be effective for the desulfurization of naphtha. Oxidation of the organosulfur compounds in NAP was confirmed by GC-FPD method as described previously 13) . The large sulfur reductions in NAPO demonstrated that most of the oxidized sulfur compounds were removed only by separation of the naphtha and AcOH phases since the oxidized sulfur compounds resided mainly in AcOH phase, possibly due to their high polarities.…”

“…Several oxidation processes for thiophenes by using formic acid _ H2O2 3) , formic acid _ H2O2-phase transfer catalyst-ultrasonication 4) , formic acid _ H2O2 _ silica gel 5) , acetic acid (AcOH) _ H2O2-quaternary ammonium coordinated ionic liquid 6) , H2O2 _ Ti-containing molecular sieves 7) , H2O2 _ titanium silicate 8)～10) , H2O2 _ Au/titanium silicate 11) , and H2O2 _ molybdophosphoric acid-phase transfer catalyst 12) have been reported. We previously demonstrated that thiophenes can be oxidized with H2O2 _ tungstophosphoric acid (TPA) in both AcOH and octane/AcOH organic biphasic systems, and that the biphasic oxidative treatment is effective for the ODS of naphtha 13) . Furthermore, we have shown that dibenzothiophenes were smoothly oxidized with H2O2 in the presence of H2SO4 in a similar organic biphasic system using AcOH as a polar solvent, due to the formation of peracetic acid (AcOOH) 14) .…”